Question on High Sierra install on ext. SSD

[ramcell]

I have External SSD with 2 bootable Sierra partitions connected by Thunderbolt to my iMac 5K . If i install High Sierra on one partition what will happen to the other partition ? Will Sierra on the other partition still be there and bootable ? Will my internal SSD Sierra boot drive be affected ?

 

[chabig]

All untouched partitions will remain untouched. Everything will work fine.

 

[oldhifi]

Yea I like to dual boot High Sierra on my Imac HD and El Captain on my ext La Cie, works great..